1. Field of the Invention
The present invention relates a mainframe computer system that is operable on one of two distinctly different operating systems. More particularly, the present invention relates to a dual purpose computer that may be loaded with one of two distinctly different operating systems and associated microcode to prepare the same computer for operation with application programs that are designed for the operating system that is loaded into the computing system.
2. Description of the Prior Art
Compilers and emulators are well known and are generally used as black box systems for converting operating instructions from one format into another format which is usable by a different computing system. Compilers and emulators have been classified in U.S. Class 364, Subclass 200 with dual mode operating system computers and microprogrammed computers which have alterable stored micro routines utilized to emulate different computers or computing systems. Such computing systems are discussed in the microprogrammable CPU described in U.S. Pat. No. 4,199,811 which has been assigned to the same assignee as the present invention. This prior art reference discusses the reasons that cause microprogrammed emulators to be generally slower than an emulated computing system which offers a desirable yet complex solution.
U.S. Pat. No. 4,791,558 describes a system for generating computing programs. This reference generally describes a compiler or emulator for adapting IBM System 370 program object modules arranged in general format to a format usable by IBM RT PC AIX operating systems of the type used on a personal computer. While this type of compiler does adapt a large library of existing programs to new architecture computers, the compiler (or modified compiler) which produces an object module having instructions for the new computing system converts the first instruction format which is not loadable into the new computing system into a second format which is loadable into the new computing system.
A more desirable, and more expensive, approach to emulation is found in the IBM AS 400 computing system which operates on two distinct operating systems. Such Dual Operating System Computers require a new architecture different from either previous architectures or systems being merged together and operate on a single new operating system. A variation of such merged operating system is described in U.S. Pat. No. 4,747,040 issued to AT&T. This dual mode operating system computer supports UNIX.RTM. and MS-DOS.RTM. operating systems in a multi-tasking computing systems. The MS-DOS operating system and its applications are executed in a real or non-protected mode and UNIX applications are executed by the UNIX operating system in a protected mode to prevent conflicting attempts to access the same peripheral device or to write in the same region of the main memory. To prevent such conflicts, special merge support hardware needs to be provided.
It would be desirable to provide a mainframe computing system which is designed for operation with a first preferred mode operating system that will efficiently execute programs designed for operation on the mainframe computing system when loaded with the first operating system. It would be further desirable to provide the same mainframe computing system with structural means which permit the computing system to be loaded with second and distinctly different operating system so that the same structural mainframe is also operable efficiently on a second and different operating system and efficiently executes these programs designed for operation by the second operating system.